GPS controlled guidance system for farm tractor/implement combination

ABSTRACT

Embodiments of the present invention comprise a system for positioning a drawn implement being pulled by a vehicle traveling generally along a desired path of movement, the vehicle having a mounting hitch on the rear end thereof where a system hitch is configured to adjust its angular orientation relative to the vehicle mounting hitch and a global positioning system receiver operable to detect the position of the implement relative to the desired path as the vehicle moves generally along the desired path and generate a signal that is indicative of the lateral position of the implement relative to the desired path and means for controlling the hitch means to adjust the angular orientation of the hitch means so that the implement follows the desired path of movement in response to the global positioning system signals.

The present invention generally relates to guidance control systems forimplements that trail a vehicle and for the vehicle that pulls theimplements.

In the farming industry, guidance systems for controlling the positionof trailing implements have been developed and marketed for many years.The design of some of the types of systems has limited theireffectiveness and accuracy with regard to positioning the implement.Guidance systems that have exhibited reliable and accurate operation arethose manufactured and marketed by Sunco of North Platte and Madrid,Nebr.

The Sunco systems are marketed under the trademark AcuraTrak haveexhibited superior operating characteristics for guiding many types oftrailing implements that are pulled by farm tractors. While someguidance systems are designed to be more concerned with controlling thetractor itself, the AcuraTrak system is designed to control the lateralposition of an implement relative to the tractor that is pulling it,with the focus being on proper positioning of the implement along adesired path as the implement is pulled through a field duringoperation. The currently marketed Acura Track guidance systems operatein a manner based on principles that are set forth in U.S. Pat. Nos.5,240,079, 5,150,849 and Re. 34,080, and are generally applicable tocertain aspects of the present invention. All of these patents arespecifically incorporated by reference herein.

The guidance systems disclosed in those patents utilize a wand mechanismassociated with the implement which is dragged along the ground and is acommon means for sensing the relative position of the implement relativeto the rows. The wand is mounted on the implement in a manner that it ispositioned in the middle of the distance between two adjacent rows. Themidpoint between two rows is usually the lowest point between the rows,since a cultivating operation tends to move dirt from the middle towardthe plants, for example. The wand is angularly moveable so that itsangular position can change depending upon whether the implement isoriented in the center between adjacent rows or is offset from thecenter. Thus, if the implement is moving to one side of center to theother, the angular position of the wand will change and providecorrective signals for controlling the guidance system to alter thelateral position of the implement relative to the rows.

It should be easily understood that if an operator is cultivating a cropthat has already reached a stand, or is planting or marking out rows, orthe like, the difficulty does not reside in the operator being able tokeep the tractor between the rows without the tractor wheels crushingthe crop, but rather keeping the implement from getting too close to thecrop which could, in the case of cultivation, result in damage to theroots of the crop by the cultivator blades. In the case of marking outrows, it is obviously desirable to have uniform rows.

The AcuraTrak System has a mechanism that attaches to the three pointhitch of the tractor and effectively lengthens one side andcorrespondingly shortens the other side to correct for lateral movementof the implement from the center of the rows. The mechanism operates incombination with a stabilizing or Coulter wheel, which is a disc-likewheel attached to the rear of the implement that engages the ground. Thestabilizing wheel provides a fulcrum about which adjustment of themechanism makes the necessary corrections to keep the implement centeredbetween the rows.

With the advent of global positioning systems (GPS), it has been thedesire, if not the goal of many in the agricultural industry to use GPSsystems as the navigation tool to control tractors during a planting orother farming operation to make and/or follow rows that are properlyaligned in a field and relative to other rows. Improvements in the GPSsignals now enables positioning within a tolerance of an inch or lessduring a farming operation, also enables accurate mapping of paths thata vehicle should travel. The combination of these capabilities hasresulted in increased success in integrating automated guidance controlsfor tractors. However, controlling the path of a tractor does notnecessarily result in the implement following the desired path.

SUMMARY OF THE INVENTION

Embodiments of the present invention comprise a system for positioning adrawn implement being pulled by a vehicle traveling generally along adesired path of movement, the vehicle having a mounting hitch on therear end thereof where a hitch means is configured to adjust its angularorientation relative to the vehicle mounting hitch and a globalpositioning system receiver operable to detect the position of theimplement relative to the desired path as the vehicle moves generallyalong the desired path and generating a signal that is indicative of thelateral position of the implement relative to the desired path and meansfor controlling the hitch means to adjust the position of the hitchmeans so that the implement follows the desired path of movement inresponse to the global positioning system signals.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D and 1E are greatly simplified top views of atractor traveling down a row and illustrating the operation of the hitchmechanism that is associated with the guidance system disclosed hereinand also showing a trailing implement that is equipped with astabilizing disc when the tractor is traveling at various angularorientations relative to the rows.

FIG. 2A is a perspective view of the rear of the system hitch that isattached to the three point hitch of a tractor and to which theimplement is to be attached.

FIG. 2B is a side view of the system hitch.

FIG. 3 is a perspective of the back of a tractor having a 3 point hitch.

FIG. 4 is a plan view of the control module of the present invention;

FIG. 5 is a perspective view of a representative steering wheel of atractor shown with a steering module for steering the tractor.

DETAILED DESCRIPTION

Broadly stated, a guidance control system for farm tractors incombination with a trailing implement is shown and described herein,although the guidance system is not limited to such a particularapplication. It is contemplated that the guidance control system couldbe used with vehicles other than farm tractors and could have generalapplicability to any such vehicle that would utilize a mounting hitch towhich some type of implement could be attached where side to sideadjustability for controlling the path of movement of the implement isdesired.

However, the system is particularly useful in guiding implements thattrail a tractor including but not limited to those used in row cropfarming. The preferred embodiment of the system disclosed herein isparticularly configured for use with a 3-point mounting hitch (alsoknown as a quick hitch) in conjunction with a coulter disc, but otherembodiments can be used with a sliding side-to-side type of adjustment,and even a a draw-type hitch. The preferred embodiment of the guidancesystem includes a system hitch that is connected to the 3-point mountinghitch and is configured to effectively extend and retract the two lowerconnections between the implement and the tractor, with the extension ofone side resulting in retraction of the other, thereby changing theangle of the guidance system hitch relative to the angle of the mountinghitch.

The preferred embodiment of the present invention is directed to asystem which is configured to operate to have an implement being pulledby a vehicle accurately follow a desired path that is defined in somemanner and stored in a memory of a GPS system. The preferred embodimenthas a GPS antenna that is mounted to the implement being drawn and it isthe operation of the GPS system to generate correction signals when theimplement veers off of the desired path.

The preferred embodiment of the guidance system does not use the GPSsystem to steer the tractor nor are the correction signals determined ina manner which causes the tractor to change course, but the correctionsignals cause the guidance system to adjust the angular orientation ofthe implement to change and thereby correct the path of movement of theimplement. This is unlike all known GPS guidance systems with regard tothe combination of a tractor and a drawn implement. All known guidancesystems merely track the course of the tractor along the desired path ofmovement or detect both the tractor and the implement by means of GPSantennas being located on both of them. In these known systems, anycorrection of the desired path is achieved by controlling the steeringof the tractor in a manner which will reduce the error in the path ofthe implement. That manner of guidance is not the manner of operation ofthe preferred embodiment of the present invention. The preferredembodiment of the present invention merely tracks the position of theimplement along the desired path and make corrections to the orientationof the implement relative to the tractor. Significantly, if the tractoris traveling along a path that is generally within the bounds ofcorrection by the implement, the implement will keep moving along thedesired path. As a consequence of keeping the implement on its desiredpath, any deviation of the tractor from the desired path can bedetermined from the implement guidance system and such determination isin the form of an electrical signal that can be used to automate thesteering of the tractor.

Referring to the drawings, and particularly FIG. 1A, a tractor,indicated generally at 10, has rear drive wheels 12 and front wheels 14for steering the same through a field having rows 16 of crop plants. Thetractor 10 has a cab 18 and a 3-point mounting hitch, indicatedgenerally at 20, comprised of left and right outer draft links 22, 24and a center link 26 for mounting implements. As shown in FIG. 3, whichillustrates an actual 3-point hitch mounted on a tractor, the left andright draft links 22, 24 are lower than the center link 26 and all ofthese links are shown to be connected to a generally upside downU-shaped frame 28, with the frame having upwardly oriented hooks 22A,24A and 26A which are configured to hook onto an implement, indicatedgenerally at 30 in FIG 1A, which has a transverse toolbar 32 and anumber of cultivating tools 34 mounted to the toolbar 32. It should alsobe understood that many implements have a toolbar to which other toolsare mounted, such as bedders, strip till machines, planters, debrisclearing tools and the like. Also, the representation of FIG. 1A doesnot illustrate the frame 28 for the sake of simplicity. However, thecurrent 3-point mounting hitches being marketed do have such a frame 28.

As is also illustrated in FIG. 1A, the lower outer 3-point links 22 and24 that are attached to the implement toolbar 32 form a generallyV-shape in that the links 22 and 24 are narrower in the front where theyattach to the tractor than the opposite end where they attach to theimplement toolbar 32. The tractor 10 also has sway blocks 36 attachedalong the length of the 3-point links 22, 24 on both sides generally atthe rear of its transmission housing 38. The sway blocks 36 can bepositioned to prevent lateral movement of the lower 3-point links 22, 24as they are lifted and lowered or can be adjusted so that the links areat least partially free to move in the lowered working position, butpermit no lateral motion in the raised or transport position.

Because of the V-shape of the links 22, 24 when they are lowered intothe working position, the 3-point links 22, 24, 26 are free to move backand forth or transversely relative to the path of movement of thetractor 10, the implement 30 tends to move on its own in a side to sidearc. If the links are not free to move, the implement 30 is held rigidto the tractor 10, the condition commonly known as “tail out” occurs. Asis particularly illustrated in FIG. 1A, if the tractor 10 is steeredleft for whatever reason, the implement 30 will move in the oppositerightward direction, and can cause damage to plants in the row by thecultivating tools 34. A “Tail out” condition is also undesirable for thereasons that it drains horsepower and creates operator fatigue.

While the illustration of FIG. 1A is intended to illustrate theenvironment of a tractor/implement combination in a field andparticularly to describe a tail-out condition, it does not illustrate aguidance system.

The preferred embodiment of the guidance system is partially illustratedin FIGS. 2A and 2B which illustrates the hitch, indicated generally at50, of the guidance system. The hitch 50 is connected to the mountinghitch hooks 22A, 24A and 26A and the implement is then attached to threepoints of the guidance system hitch 50, such as left guidance hitch hook52 that is shown in the side view of FIG. 2B.

Referring to FIG. 2A, which shows the guidance system hitch 50 from thefront end, i.e., the end which attaches to the tractor 10, the hitch 50has a left side casting 54, a right side casting 56, which respectivelycontain left and right hydraulic cylinders 58 and 60. The cylinder 58has an extendable piston 62 whereas the cylinder 60 has a similar piston64, with each of the pistons being connected to crank arms 66 and 68,respectively, each of which pivots around a shaft such as the rightshaft 70, the left not being shown. The crank arms 66 and 68 have amounting pin 72 for attachment to the mounting hitch 20. A centerclevis, indicated generally at 74, also mounts to the middle hook 26A ofthe 3-point mounting hitch 20. The cylinders 58 and 60 are connected toa hydraulic system, generally contained within the box 76, which ispreferably connected to the hydraulic system of the tractor. The boxalso contains a hydraulic valve that controls the position of thecylinders as a function of the control signals that are generated by theGPS control module. The hydraulic lines are preferably connected so thatextension of one cylinder 58 will result in displacement of fluid fromone end of the cylinder and will cause a similar displacement in theopposite cylinder 60 to result in comparable retraction of its piston64. Movement of the pistons 62 or 64 will rotate the crank arms 66 or 68around their shafts and by virtue of the connection with clevis pins 72,result in movement of one side or the other toward and away from thetractor to thereby change the angular orientation of the guidance systemhitch 50 relative to the tractor 10.

To measure the position of the crank arms 66 and 68 and thereby theangular orientation of the guidance system hitch 50, a hitch anglesensor mechanism, indicated generally at 80, is provided and itcomprises a rotatable arm 82 that is connected to the crank arm 66 andpivots around a potentiometer 84 which generates an electrical signalthat is indicative of the angular position of the arm 82. Since the arm82 is connected to the crank arm 66, the sensor mechanism 84 provides asignal that is indicative of the position of the crank arm 66, which inturn is indicative of the angular orientation of the hitch 50 relativeto the mounting hitch 20.

It should be understood that if the hitch 50 is centered, the crank arms66 and 68 will be in the same longitudinal position, i.e., the distancefrom the left and right clevis pins 72 to the respective left and righthooks 52 will be the same. This means that the implement 30 isnecessarily straight behind the tractor 10. If the implement 30 iscentered between the rows 16, it also means the tractor 10 is travelingdown a path so that the wheels are centered between adjacent rows 16 asis desired. Importantly therefore, when the guidance system is operatingto maintain the implement traveling along the desired path “centered”between the rows, the potentiometer 84 signal is proportional to thepath of the tractor 10. If the guidance system requires a correction tokeep the implement on a desired path, it will cause the crank arms 66and 68 to adjust and such an adjustment will cause the potentiometer 84to generate a signal that can be used to steer the tractor 10 itself.

Returning to FIGS. 1A through 1E, these diagrammatic representationsshow the guidance system hitch 50 mounted on the tractor 10 and alsoshow a stabilizing or coulter disc 88 that is attached to and carried bya frame structure 90 that is preferably mounted to the implement toolbar32 and located some distance behind the toolbar 32. This stabilizingdisc 88 penetrates into the soil and acts as a fulcrum about which theimplement 30 can be angled. Stated in other words, when the angle of thehitch 50 is changed, it slightly changes the angular orientation of thestabilizing disc 88 and causes the implement 30 to be transversely movedduring forward movement to bring the implement 30 back to center alongthe desired path of movement. It should be understood that while it ispreferred that a stabilizing disc 88 be used, a stabilizing wheel mayused in some applications. It may be possible that some implements maynot require a stabilizing disc at all, provided that the naturaloperational characteristics of the implement be such that the implementwould tend to rotate in the same way as if a stabilizing disc 88 werepresent. Establishing a stable fulcrum is very important with thepreferred embodiment of the present invention.

The illustration of FIG. 1B shows the tractor 10 moving down the rows ina centered position wherein the rear and front wheels 12, 14 aretraveling midway between adjacent rows 16 and the implement 30 issimilarly centered. In this circumstance, the effective length of theleft and right linkages are equal, and the toolbar 32 is perpendicularto the direction of the rows. The desired path of the implement 30 isbeing followed. It should be understood that the term “effective length”of one of the linkages means (for the left linkage, for example) thelength of the link 22 plus the distance between the clevis pin 72 andthe hook 52. The latter distance varies as the clevis arm 66 is rotatedby operation of the cylinder 58.

In FIG. 1D, the tractor is shown beginning to move left of the desiredpath. As this occurs, the links 22, 24, 26 swing left, the cylindersmove to increase the effective length of the right linkage 24 anddecrease effective length of the left linkage 22. If the operator steersthe tractor so that the tractor stays left of the desired path as shownin FIG. 1C, the cylinders generally maintain the effective lengths ofthe linkages so that the implement maintains its centered position eventhough the tractor is not centered.

If the desired path is curved as often occurs when operating in landcontours, FIG. 1E illustrates that as the tractor moves on a contour tothe right, the cylinders increase the effective length of the leftlinkage 22 and shorten the effective length of the right linkage 24.Depending on the severity of the curve of the contour, the action of thecylinders and linkages will continue at varying degrees around thecontour always keeping the implement toolbar 32 perpendicular to thedesired path and pointed toward the center of the contour. The oppositeaction takes place on a left contour. As the contour straightens, thecylinders will equalize the effective lengths of the linkages as thetractor moves to the correct position in relation to the desired path.

Thus, with the corrections that are made by the guidance system, thetractor 10 does not have to be precisely maintained along the desiredpath and the system will maintain the implement 30 centered relative tothe rows 16. When the angle of the guidance system hitch 50 is changedrelative to the mounting hitch 20, it is also important that the links22, 24, 26 of the mounting hitch 20 be free to move from side to side bya predetermined amount, preferably about 10 inches. This permitsangulation of the system hitch 50 to result in the centering movement ofthe system hitch 50 as well as the rear portion of the mounting hitch 20relative to the lateral position of the tractor 10 itself.

The system includes a control console 100 that is preferably installedinside the cab 18 of the tractor 10. This console 100 has a digitaldisplay 102 that can provide important information relating to thestatus and operation of the system. More particularly, it can describenecessary steps in the operation of the system as well as diagnosticchecks of the system. It can provide a scrolling functionality as wellas static messages. The console 100 also has a illuminated bar graph104, an on button 106, an off button 108 and a menu/exit button 110. Inaddition, a cluster of five buttons 112 are provided which performdifferent functions depending upon menu selections.

With regard to the bar graph 104, it includes a pair of green bars 114,a set of five yellow bars 116 located on opposite sides of the greenbars 114 and a pair of red bars 118 located on each end. These barseffectively provide an indication of the position of the tractor 10relative to the implement 30 during operation, with the green bars 114being illuminated if the tractor is centered, the yellow bars beingilluminated if the tractor is deviating from center, with the number ofbars being proportional to the amount of deviation. The red bars 118indicate that the tractor has deviated from center by an amount that isbeyond effective control or reliable operation.

The signals that control the bars that are illuminated originate fromthe sensor 80 that monitors the angular position of the crank arm 66.With regard to the cluster of keys 112, these keys allow the centerposition of the system to be manually offset to the left or right. Thisis done by pressing either one of the left or right arrow keys. Bypressing the left arrow key, it will offset the center to the leftwhereas the right arrow will offset the center to the right. The systemwill then operate from the offset center position until it is changed orrestored to the true center. Pressing the centering key i.e. the keybetween the left and right arrows, will immediately bring the hitch 50back to the true center.

The menu key 110 allows adjustment of operating parameters, diagnosisand calibration of the system, among other actions. By pressing the menukey, the menu is opened and the up and down arrow keys of the cluster112 can be used to scroll through the menu items. In this mode ofoperation, the right arrow and left arrow keys can be used to changeindividual settings of parameter and the center key can then be used tolock-in the settings. To exit the menu, the menu key is again pressed.While this matter of operation is preferred, it should be understoodthat other functionality and operating procedures can be implemented.

The signal that is used to control the bar chart 104 originates from thesensing hitch angle sensor mechanism 80, and as previously described,this hitch angle sensor mechanism effectively determines the centerposition of the tractor 10, assuming that the guiding system has theimplement 30 in its centered position. The signals can be used by atractor steering mechanism to keep the tractor in a centered position,provided the implement is being controlled to maintain its movementalong the desired path during operation. It should be understood thatalthough the GPS system is used to guide the implement along the desiredpath in the preferred embodiment, and that the hitch angle sensormechanism 80 effectively determines the center position of the tractor10, and therefore can be used to steer the tractor, the hitch anglesensor mechanism 80 can also be used to steer the tractor even if theimplement guidance is carried out using the traditional wand mechanismsrather than a GPS system.

Referring to FIG. 5, the sensor mechanism signals can be used inconnection with a commercially available product that is marketed underthe trademark EZ-STEER that is manufactured and marketed by the TrimbleCompany of Sunnyvale, Calif. This mechanism has a steering module 120that is mounted to a steering column 122 of a steering wheel 124. Themodule 120 has a rotatable output shaft 126 with a soft rubber outercovering 128 that engages the steering wheel of a tractor. It also has aretractable mechanism that enables the module to be moved into and outof engagement with the steering wheel. Using the sensor mechanismsignals to rotate the output shaft 126 in the clockwise orcounterclockwise direction will rotate the steering wheel 124accordingly for steering the tractor. While the illustration of FIG. 5is intended to be representative of a tractor, it is apparent that onlya steering wheel and associated components is actually shown togetherwith the steering module 120. It should also be understood thathydraulic steering mechanisms are also commercially available that tieinto the hydraulic steering circuitry to steer the tractor and whilesuch mechanisms are more expensive, they may be used in place of the EZSTEER mechanism.

With regard to the GPS system that is to be used in the system of thepresent invention, it should be understood that the present inventionutilizes a GPS system, rather than having invented it. There are severaltypes of GPS systems that have been developed and marketed and whichhave been employed in implementations relating to agriculturalapplications. Some of the systems that have been utilized to dateinclude the RTK (Real Time Kinematics) system that uses a base stationand GPS to typically provide a plus or minus one inch accuracy. Othersystems that may be used include the DGPS HP (Differential GPS HighPerformance) system that typically provides accuracy to plus or minusfour inches. This version utilizes a GPS satellite signals for basiclocation information and requires a least an OmniSTAR HP satellitecorrection signal subscription for each system. Other systems include aDGPS (Differential GPS) system that typically provides accuracy toapproximately plus or minus ten inches. This version utilizes GPSsatellite signals for basic location information and requires at leastan OmniSTAR VBS satellite correction signal subscription for each systemor the pre-WAAS signal which is differentiated by the source ofcorrection signal.

It is preferred that the system used with the present invention be themost accurate possible. Because a cultivator, for example, can cutplants from rows as a result of a deviation of only a few inches, theRTK system which has a plus or minus one inch accuracy is preferred overthe other above-described systems. To the extent that other systemsexist which are more accurate than plus or minus one inch, they arepreferred for the reason that such close tolerances can be veryimportant with regard to the successful operation of a guidance systemin certain applications.

Since the present invention controls the implement along the preferredpaths, a GPS antenna 130 is preferably located on the implement and moreparticularly on the center of the tool bar 32 of the implement 30.However, it should be understood that it may be located away from centerprovided offsets are calculated as may be necessary. It may also bebeneficial to have the GPS antenna 130 mounted on a structure that isforward of the tool bar by a few inches or more so that some lead timein the position of the path is gained, which would enable timelycorrection of the path of the implement. Although not shown, it shouldbe understood that the antenna 130 is in communication with a GPScontrol module located within the cab. Such communication between thecontrol module and the antenna can be accomplished by conductorsextending between the two or by a wireless communication link, such as aBluetooth or other type of communication link.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the following claims.

1. Apparatus for positioning a farm implement of the type which has anelongated transverse tool bar to travel along a desired path of movementwhile being drawn by a motor vehicle moving generally along the path,the vehicle having a mounting hitch on the rear end thereof, saidapparatus comprising: hitch means for attachment to the hitch of thevehicle and configured to have the implement mounted thereto, said hitchmeans having hydraulic means for selectively adjusting the orientationof said hitch means relative to the mounting hitch, the tool bar beingoperatively attached to said hitch means; a global positioning system(GPS), said GPS including a receiver and an antenna, said antenna beingmounted near or forwardly of the tool bar, said GPS being operable todetect the position of the tool bar relative to the desired path as thevehicle moves forwardly generally along the desired path and generate asignal that is indicative of said lateral position means for controllingsaid hydraulic means to adjust the orientation of said hitch means sothat the implement follows the desired path of movement in response tosaid signals from said global positioning system receiver.
 2. Apparatusas defined in claim 1 wherein said orientation of said hitch meansfurther comprises the horizontal angular orientation of said hitchmeans.
 3. Apparatus as defined in claim 2 wherein said hitch means isconfigured to selectively retract and extend each side of the hitchmeans generally horizontally relative to the mounting hitch of thevehicle to thereby adjust the angular orientation of said hitch meansrelative to the mounting hitch.
 4. Apparatus as defined in claim 2wherein the vehicle mounting hitch is a three point hitch.
 5. Apparatusas defined in claim 4 wherein said first sensing means produces a signalthat is indicative of the position of the vehicle relative to thedesired path.
 6. Apparatus as defined in claim 1 wherein said antenna isoperatively connected to the center of said tool bar.
 7. Apparatus forcontrolling the position of an implement of the type which has anelongated transverse tool bar being drawn by a tractor relative to adesired path of movement while the tractor travels forwardly generallyalong the path, the tractor having at least a two point mounting hitch,said apparatus comprising: hitch means for attachment to the mountinghitch of the tractor and configured to have the implement mountedthereto, said hitch means having hydraulic means to adjust the angularorientation of said hitch means relative to the mounting hitch byselectively retracting and extending both sides of the hitch means in agenerally horizontal direction relative to the mounting hitch of thetractor wherein the extension or retraction of one side results in acorresponding retraction and extension of the other side; a globalpositioning system having a receiver and an antenna, said antenna beingoperatively connected near or forwardly of the tool bar of the implementfor detecting the position of the tool bar relative to the desired pathas the tractor moves generally along the desired path and generatingcorrection signals indicating deviation from the desired path; controlmeans responsive to said correction signals for operating said hydraulicmeans to selectively extend or retract each side of said hitch means. 8.Apparatus as defined in claim 7 wherein said apparatus furthercomprises: hitch sensing means for sensing the orientation of said hitchmeans relative to the mounting hitch and generating a position signalindicative of said sensed orientation; means responsive to said positionsignal for steering the tractor along the predetermined path. 9.Apparatus as defined in claim 8, wherein said steering means comprises amotor having an output shaft with a mechanism that is configured toengage and selectively turn a steering wheel of the tractor to steer thesame.
 10. Apparatus as defined in claim 8 further comprising a displaymodule for displaying the instantaneous position of the tractor relativeto the desired path.
 11. Apparatus as defined in claim 10 wherein saidinstantaneous position is displayed as a bar graph.
 12. Apparatus asdefined in claim 8 wherein said global positioning system receiver ismounted on said implement.
 13. Apparatus for controlling the position ofa farm implement of the type which has an elongated transverse tool baras the implement is drawn by a tractor so that the implement follows adesired path of movement as the tractor moves generally forwardly alongthe path, the tractor having a three point mounting hitch, saidapparatus comprising: hitch means for attachment to the three pointmounting hitch of the tractor and configured to have the implementmounted thereto, said hitch means having hydraulic means to adjust theangular orientation of said hitch means relative to the mounting hitchby selectively retracting and extending both sides of the hitch means ina generally horizontal direction relative to the mounting hitch of thetractor, wherein the extension or retraction of one side results in acorresponding retraction and extension of the other side; first sensingmeans for sensing the angular orientation of said hitch means relativeto the mounting hitch and generating a first signal indicative of saidsensed orientation; a global positioning system having a receiver and anantenna wherein at least said antenna is located near or forwardly ofthe tool bar, said system being operable to detect the position of theantenna relative to the desired path as the tractor moves generallyalong the desired path and generate a second signal that is indicativeof said lateral position; means for controlling said hydraulic means toadjust the angular orientation of said hitch means so that the implementfollows the desired path of movement in response to said second signalsfrom said global positioning system.
 14. Apparatus as defined in claim13 wherein said signal that is indicative of said sensed orientation isdirectly proportional to the lateral position of the tractor relative tothe desired path.
 15. Apparatus for positioning a farm implement of thetype which has an elongated transverse tool bar that is operativelyattached to hitch means to travel along a desired path of movement whilebeing drawn by a motor vehicle as the vehicle moves generally along thepath, the vehicle having a mounting hitch on the rear end thereof, saidapparatus comprising: hitch means for attachment to the hitch of thevehicle and configured to have the implement mounted thereto, said hitchmeans having hydraulic means for selectively adjusting the orientationof said hitch means relative to the mounting hitch; first sensing meansfor sensing the orientation of said hitch means relative to the mountinghitch and generating a first signal indicative of said sensedorientation; a global positioning system having a receiver and anantenna operable to detect the position of the implement relative to thedesired path as the vehicle moves forwardly generally along the desiredpath and generate a second signal that is indicative of said lateralposition, said antenna being mounted in a location that detects theposition of the tool bar relative to the desired path; means forcontrolling said hydraulic means to adjust the orientation of said hitchmeans so that the implement follows the desired path of movement inresponse to said second signals from said global positioning systemreceiver; hitch sensing means for sensing the orientation of said hitchmeans relative to the mounting hitch and generating an orientationsignal indicative of said sensed orientation; and means responsive tosaid orientation signal for steering the tractor along the predeterminedpath.
 16. Apparatus for positioning a farm implement to travel along adesired path of movement while being drawn by a motor vehicle as thevehicle moves generally along the path, the vehicle having a mountinghitch on the rear end thereof, said system comprising: hitch means forattachment to the hitch of the vehicle and configured to have theimplement mounted thereto, said hitch means having hydraulic means forselectively adjusting the orientation of said hitch means relative tothe mounting hitch; wand means operable to detect the lateral positionof the implement relative to the desired path of movement as the vehiclemoves forwardly generally along the desired path and generate a lateralposition signal that is indicative of said lateral position; means forcontrolling said hydraulic means to adjust the orientation of said hitchmeans so that the implement follows the desired path of movement inresponse to said lateral position signals from said wand means; hitchsensing means for sensing the orientation of said hitch means relativeto the mounting hitch and generate a orientation signal indicative ofsaid sensed orientation; and means responsive to said orientation signalfor steering the vehicle along the predetermined path.